Pest Profile

Photo credit: April Nobile, California Academy of Sciences (Specimen CASENT0005718; from https://www.antweb.org)

Common Name: Western harvester

Scientific Name: occidentalis

Order and Family: Order ; Family Formicidae

Size and Appearance:

Length (mm) Appearance Egg

Larva/Nymph

Adult Workers range Pogonomyrmex harvester are characterized by broad, from 5 – 7 mm boxy heads, 12-segmented antennae, a two-part waist, a pair of dorsal spines and a stinger. Many species have a set of long hairs (called a psammophore) on the posterior lower portion of the head, behind the mouthparts.

The Western is light to medium red and shiny, often with a slightly lighter gaster (last few segments of the abdomen). These ants are highly sculptured with punctate texture on the head and thorax. The thorax also has lines of texture (rugae).

The colonies have one queen (monogynous).

Queens are similar to workers but larger with a larger thorax.

Female and male reproductive ants have wings. Pupa (if applicable)

Type of feeder (Chewing, sucking, etc.): Chewing

Host(s): Harvester ants in the Pogonomyrmex specialize in seeds but may forage on other foods (generalist and opportunistic).

Description of Damage (larvae and adults): Because theses ants primarily eat seeds (up to 90% of the diet), they are pests of agricultural systems, damaging crops but especially grasslands (pasture). They harvest seeds, defoliate plants, and remove young and old plants. The Western harvester ant primarily affects the range by their clearing and feeding activities.

They also have a potent sting that causes persistent pain. The venom is considered the most toxic of venoms and its effects may spread through the lymphatic system. The venom may cause severe allergic reactions, other serious problems, and death of livestock, pets, and people. These ants sting in defense of the nest, so avoiding the nest area is a good idea.

They nest in open areas and also like some disturbance, like mowed lawns, and so are commonly found in lawns, playgrounds, managed fields, and along roads and sidewalks. The external nest area can be quite large, up to 2 m in diameter, and are easy to locate because the area is denuded of vegetation. Their nests may cause problems for livestock and harvesting equipment and contribute to soil erosion and other problems.

The western harvester ant is found in the USA, including Arizona, California, Colorado, Idaho, Kansas, Montana, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Wyoming, and Utah.

References: Cole, A.C. (1968). Pogonomyrmex harvester ants: a study guide of the genus in North America.

Klotz, J., Hansen, L., Pospichil, R. & Rust, M. (2008). Urban ants of North America and Europe: identification, biology, and management. Ithaca, NY: Cornell University Press.

Schmidt, J.O. (2003). Venoms. In R.H. Resh & R. T. Carde. (Eds.) Encyclopedia of (1160 – 1163). Amsterdam: Academic Press.

Taber, S.W. (1998). The world of the harvester ant. College Station, Texas: Texas A&M University Press.